It is known to provide stepwise adjustment mechanisms for chairs. For example, in U.S. Pat. No. 4,662,682 to Maurel, the chair base has a notched arm which may receive teeth extending from a plunger supported on the chair backrest to adjustably lock the backrest in place. A similar arrangement with a toothed lever in place of a plunger is shown in U.S. Pat. No. 4,139,235 to Elbert. In U.S. Pat. No. 4,043,592 to Fries, a pin extends from the arm of the chair back, while a notched pin latching lever is carried by a backrest bracket.
A horizontal adjustment mechanism for armrests is disclosed in U.S. Pat. No. 4,662,681 to Favaretto. The armrests of the chair are bolted onto the bottom of the seat portion of the chair and are adjustable by loosening the bolts which sit in slots, moving the armrest so that the bolts slide along the slots, and then tightening the bolts again.
Australian Patent AU-B-76302 to Ryner teaches a vertical armrest adjustment mechanism with a locking pin spring biased into one of a series of overlapping slots to lock the armrest in position.
Known adjustment mechanisms suffer from one or more of the following drawbacks. They may not allow for adjustment horizontally. They may require many parts and are often difficult to manufacture and difficult to operate. Many cannot be adjusted by the operator of the chair while seated in the chair. Many of the devices do not permit easy disassembly for maintenance, field repair or replacement. Because it is often difficult to take the mechanism apart, many of such devices do not permit adapting the chair for different user requirements. Further, many of the devices are bulky, which is problematic where a mechanism is mounted under the seat since, due to the many desirable adjustment mechanisms which must be accommodated under the seat, space is scarce.